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According to Livescience, 'Sinking cold air causes warm, moist air on the planet's surface to climb to higher altitudes, where the moisture condenses into cloud form.'

Bonnie Mask captured this roll cloud on camera--not caused by a thunderstorm in this rare instance

Kim Cunningham, a meteorologist for the Weather Channel, told Yahoo,' This is fairly rare, by the way, to have these things and see these things,especially when not associated with a thunderstorm. ... It's pretty cool though, and it probably freaked a lot of people out.'

Roll clouds are also extremely rare. Mask told Yahoo news, 'There was some cool air that blew over as the cloud blew over the house,' she said, adding that it was 'kind of strange.'

Todd Mask described the cloud in his wife's footage as, 'rolling like an ocean wave' and 'like a horizontal vortex.'

Sometimes roll clouds are mistaken for UFOs.

Todd Mask and his wife Bonnie called the phenomenon that blew over Texas 'kind of strange.'